a book in the Could You Ever? series by David Darling

Glossary

billion

One thousand million, or 1,000,000,000.

black hole

A region of space where the pull of gravity is so strong that nothing, not
even light, can escape. One way that black holes are thought to form is
when the cores of very massive stars fall in upon themselves.

combustion chamber

The part of a rocket engine in which the fuel is burned to produce exhaust
gases that drive the spacecraft forward.

electron

A tiny, negatively-charge particle, even smaller than a proton or neutron.

exhaust

The waste material produced when a fuel is burned. The reactive force arising
from the exhaust as it escapes from the combustion chamber causes a spacecraft
to gain speed.

exhaust speed

The speed at which the exhaust material from a rocket engine leaves the
spacecraft. A high exhaust speed is important if the spacecraft's final
speed is also to be high.

fusion

A process in which the most basic particles, or nuclei, of a lighter substance
combine to make nuclei of a heavier substance. During nuclear fusion, a
small amount of mass is transformed into a very large amount of energy.
The most common and energy-rich fusion reaction is that in which hydrogen
nuclei collide, at high temperatures, and create helium nuclei.

galaxy

A very large collection of stars. Galaxies come in a variety of shapes –
round, oval, spiral, and odd-shaped – and a variety of sizes. Spiral
galaxies, such as the one we live in, contain huge amounts of loose gas
and dust from which future stars may be made.

gravity

A force exerted by any object that has mass. The Earth's gravity is the
force that prevents the atmosphere,and people, from floating away into space.

helium

The second lightest and second most common substance in the universe; normally
found as a gas. At high temperatures, as in the center of stars, hydrogen
will fuse to form helium, producing huge amounts of energy in the process.

hydrogen

The lightest and most common substance in the universe; normally found as
a gas. At high temperatures, as in the center of stars, hydrogen will fuse
to form helium, producing huge amounts of energy in the process.

interstellar

A word meaning "between the stars."

interstellar ramjet

A type of spaceship in which the fuel (mainly hydrogen) is gathered and
compressed from the interstellar space ahead of the ship, using a powerful
magnetic scoop.

laser

A device used for producing concentrated, well-directed beams of very pure
light. The waves of light in a laser beam are exactly in step with one another
and all of the same length. The first laser, built in 1960, used a rod-shaped
crystal of ruby.

light-year

The distance traveled by light, moving at 186,282 miles per second, in one
year. It equals 5.85 trillion miles.

magnetic field

A region in which a force of magnetism acts.

mass

Anything that contains matter – for example, a rocket, a star, or
a person – has mass. Mass gives a measure of how difficult it is to
start moving an object that is still, or to change the speed of an object
that is already moving.

payload

The part of a spacecraft that does not include the fuel or propulsion system.
In the case of a robot probe, the payload consists largely of scientific
and communications equipment. In a spaceship with astronauts, though, a
large part of the payload is made up of the support systems and living quarters
for the human crew.

planet

A round object, usually at least several thousands miles across, that is
in orbit around a star. Planets give off no light of their own and are much
cooler than stars. The Sun has eight planets and a number of dwarf planets
(including Pluto). Many other stars also have systems of planets.

propulsion system

The means by which a spacecraft (or any other vehicle) is made to move.

solar system

The name given to the Sun and everything that goes around it, including
the planets and their moons.

star

A round, gassy object in space that normally makes its own light and heat
by nuclear fusion. The only exceptions are "dead" stars, such as white dwarfs,
neutron stars, and black holes, that have used up their supplies of fusion
energy.

theory of relativity

Developed by the great German-American scientist Albert Einstein in the
early part of the twentieth century. The so-called special theory of relativity
shows how quantities such as mass, length, and time change when objects
move at different relative speeds. In his general theory of relativity,
Einstein describes a new theory of gravity.

thrust

In rocketry, the forward force produced by a spacecraft's engine.

trillion

One million million, or 1,000,000,000,000.

weight

The downward force acting on an object due to gravity. A person's weight,
for instance, would be different on the Moon than on Earth because the pull
of gravity is different. That person's mass, though, would stay the same
wherever he or she was in the universe.